[hpsdr] Fwd: Re: AW: Advantages/Disadvantages of Pin diode switching?

[Kjell Karlsen]

------- Videresendt melding -------
Fra: "Kjell Karlsen" <la2ni at online.no>
Til: "Helmut, DC6NY" <dc6ny at gmx.de>
Cc:
Emne: Re: AW: [hpsdr] Advantages/Disadvantages of Pin diode switching?
Dato: Tue, 04 Jun 2013 12:15:53 +0200

Hi Helmut.

Yes I measured the isolation between the ports but I did not find them so
I had to do it again today!

I measured only the isolation between antenna and RX. It is -79 dBc on 50
MHz and down to 3 MHz and then decreasing to -62 dBc at 1,8 MHz.

It is difficult to measure the isolation between the TX and RX as I have
to desolder the PA transformer but I think it must be the same. The TX
signal is present on the same side as the antenna.

73, Kjell



På Tue, 04 Jun 2013 10:46:40 +0200, skrev Helmut, DC6NY <dc6ny at gmx.de>:

> Hi Kjell,
>
> did you also measure the isolation between the ports?
>
> 73, Helmut, DC6NY
>
> -----Ursprüngliche Nachricht-----
> Von: hpsdr-bounces at lists.openhpsdr.org
> [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Kjell Karlsen
> Gesendet: Dienstag, 4. Juni 2013 09:43
> An: hpsdr at lists.openhpsdr.org
> Betreff: Re: [hpsdr] Advantages/Disadvantages of Pin diode switching?
>
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Greg.
>
> If you look at the schematics for the Elecraft KPA500 TR Switch, you will
> see that they use e 1N5408 in the TX path. The bias current is not more  
> than
> 500 mA as it is driven from 5V via a 10 Ohm resistor.
>
> In Apollo ( max power measured= 25W PEP at 20V Vdd) I am using a Pin
> diode(MA4P7102F) with 35 mA bias but I have tested with S1M, a normal  
> 1000V
> silicone diode and I see no difference. The loss is around 0,5 dB in  
> both.
>
> 73, Kjell
>
>
>
>
>
> På Mon, 03 Jun 2013 11:59:33 +0200, skrev Greg - ZL3IX  
> <zl3ix at inet.net.nz>:
>
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> The important difference between PIN diodes and ordinary diodes is the
>> bias current required in the ON state.  For ordinary diodes the bias
>> current must exceed the peak signal current, otherwise the diode will
>> switch off during the negative peak of the signal.  For 10 W in a 50
>> ohm system the peak current is 632 mA, so you would need upwards of
>> 700 mA DC to hold the diode on.
>>
>> That is not true for PIN diodes, which are designed for slow turnoff.
>> Provided that the carrier lifetime of the PIN diode in use, is longer
>> than a half cycle, you only need enough current to keep the on
>> resistance reasonably low.  But beware, check the carrier lifetime
>> carefully.  Use on the lower HF bands needs really long lifetimes.
>>
>> Use of any diode switching in circuits intended for SSB, needs care,
>> as there is great potential for introducing intermod distortion. Use a
>> spectrum analyser or spare Mercury/Hermes module to check your
>> transmitted spectrum.
>>
>> 73, Greg, ZL3IX
>>
>>
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